1. Field of the Invention
The present invention relates to an etching method and apparatus using RIE (reactive ion etching). For example, the invention can be utilized in a semiconductor device manufacturing process.
2. Description of the Related Art
Conventionally, RIE (reactive ion etching) is known as an anisotropic dry etching method. As shown in FIG. 4A, in RIE, a sample 403 to be etched is provided on the side of a feeder electrode 402 to which a high-frequency power supply 404 is connected. Hich-frequency discharge is caused between the feeder electrode 402 and a grounding electrode 401 (in this example, a chamber of the apparatus serves as this electrode) that is kept at the ground potential, to perform vertical, anisotropic etching on the sample 403.
In the arrangement of FIG. 4A, a potential profile as shown in FIG. 4B is established in the state of high-frequency discharge. If CF.sub.4, NF.sub.3, CCl.sub.4, or the like are used as an etching gas, fluorine ions (F+) or chlorine ions (Cl+) is accelerated toward the sample 403 side by a negative, deep self-bias near the feeder electrode 402, to effect vertical, anisotropic etching.
FIGS. 2A and 2B show an etching process performed with the above etching apparatus. FIG. 2A shows a structure having, on a glass substrate 201, an active layer 202 of a thin-film transistor, a gate insulating film 203 covering the active layer 202, and a gate electrode 204 provided on the gate insulating film 203. As shown in FIG. 2B, the exposed portions of the gate insulating film 203 are removed by RIE in which the gate electrode 204 used as a mask.
However, in the process of FIGS. 2A and 2B, it frequently occurs that the gate insulating film 203 is broken electrically. This is considered to be caused by an instantaneous application of a negative. deep bias voltage (as deep as minus several hundred volts under certain conditions) occurring near the feeder electrode 402 (see FIG. 4B) at the start of RIE.
That is, it is considered that at the start of etching a high voltage that is instantaneously applied between the exposed gate electrode 204 and the active layer 202 that is covered with the gate insulating film 203 causes electrostatic breakdown of the gate insulating film 203.
A similar phenomenon also occurs at the end of the etching step. This is considered as a phenomenon due to a fast variation of the voltage being applied to the sample when the bias voltage of the sample is removed.